CONTENTS 1. General .…………………………………………………………………………………… 3 2. Principle of Operation ….……………………………………………………………... 4 2. 1. Mechanisms ….……………………………………………………………… 4 2.1.1. Headblock ..……………………………………………………… 4 2.1.2. Erase Head ..……………………………………………………… 5 2.1.3. Double Capstan Tape Drive ………………………………… 5 2.1.4. Mechanism Control Cam Operation ………………………… 6 2. 2. Amp. Circuits ….……………………………………………………………… 7 2.2.1. Playback Eq. Amp. Circuit …..………………………………… 7 2.2.2. Record Eq. Amp. Circuit …………………………………………… 9 2.2.3.
5. 10. Record Switch Linkage Adjustment ………………………………………………………… 29 5. 11. Flywheel Holder Adjustment ……………………………………………………………… 30 5. 12. Eject Wire Adjustment ………………………………………………………………………… 30 5. 13. Lubrication …………………………………………………………………………………… 30 6. Parts Location for Electrical Adjustment ………………………………………………………… 31 7. Electrical Adjustments and Measurements ……………………………………………………………… 32 7. 1. Adjustment and Measurement Instructions ………………………………………… 32 7. 2.
2. PRINCIPLE OF OPERATION 2.1. Mechanisms 2.1.1. Headblock Refer to Fig. 2.1.1 Headblock. Nakamichi 481 Headblock provides more stabilized tape travel. Accuracy of tape travel is one of the most essential factors for a device to optimize its performance.
level on the both Level Meters. This system has also been carefully designed so as to minimize influence each other between azimuth and height adjustment. 2.1.2. Erase Head Fig. 2.1.3 shows the sectional view of the Erase Head. Fig. 2.1.4 shows the characteristics of erasing current and erasure. assembled with the Head Base. It is installed with three screws.
positioned perfectly vertical to the tape surface. Otherwise, the running tape might become out of the tape guide resulting in irregular movement. 2.1.4. Mechanism Control Cam Operation Refer to Fig. 2.1.6 Mechanism Control Cam timing chart. Function of N-481 Mechanism is done by Cam Control. Cam is driven by the Control Motor.
(3) F.F. or Rewind Mode By pressing the F.F. or Rewind Switch, it comes either to F.F. or Rewind mode. The only difference of these two modes is that one is to turn the Reel Motor reverse and the other to transmit the torque against the Reel Hub onto the take-up side or to the supply side. Brake is re leased at this stage and the Reel Motor begins to turn F.F. or Rewind. 2.2. Amp. Circuits 2.2.1. Playback Eq. Amp. Circuit Fig. 2.2.1 shows the playback equalizer amp. circuit. Fig. 2.2.
It is specified in the IEC Standard that the time constant is 120 us on tapes of ferric oxide, and 70 us on tapes of Cr02. However, in the case of Eq. Switch on N-481, when time constant at playback is changed, at the same time constant at record must also be changed. Therefore, even though record and playback is made by the method other than the IEC Standard, no deterioration of frequency response or level difference will occur.
2.2.2. Record Equalizer Amplifier Circuit The record equalizer amplifier circuit consists of the Out put Amp. incorporated in the Dolby NR IC and peripheral circuits as shown in Fig. 2.2.4. VR102, VR103, and VR104 are the record calibration semi-fixed volumes for ZX, SX and EX tapes. The output of the Output Amp. is given to these volumes, and the outputs from the volumes are fed back to the inverting input of the Output Amp. via amplifier Q103 and a time-constant changeover circuit.
2.3. Mechanism Control Circuits 2.3.1. Outline (1) Control Button Operation Record, Rewind, Stop, Play, and Fast-Forward Buttons consist of a 5—way switch and are interlocked each other. When one button is pressed, it is mechanically locked in the ON state and other buttons are mechanically released. Stop Button is of momentary type and acts to release other buttons mechanically. But it is not used to control circuits electrically. Pause Button is independent from others and is of push-on and push-off type.
2.3.2. +12 V Power Source Refer to Fig. 2.3.2 circuit diagram. Only +24 V DC power supply is used in the N-481. The circuit acts to produce a +12 V power source from the +24 V DC power supply. Mechanism control is done by using thus produced +12 V. 2.3.3. Power-mute Signal Refer to Fig. 2.3.3 circuit diagram and Fig. 2.3.4 timing chart. Power-mute = L signal is produced pulse-likely when Power Switch is turned ON or OFF.
(a) Reached tape-end during PLAY (PLAYBACK or RECORD), FF, or REW mode Explanation is made for PLAY mode as an example. For FF or REW mode, the shut-off function is the same as for PLAY mode. As Play Button is locked ON mechanically, Kplay = L. Accordingly, R488 (100 kohm) is grounded through Play Button and the voltage at the point A becomes approx. +23 V. Since the voltage at the point A is not lower than the emitter voltage of Q424, Q424 is turned OFF and Q426 is also turned OFF.
(b) Mode is changed 1) From FF to REW mode, or vice versa, or from FF to PLAY mode Refer to Fig. 2.3.7 timing chart. When mode is changed from FF to REW mode, or vice versa, or from FF to PLAY mode, momentary STOP mode is automatically taken in view of the response of the tape deck mechanism, and after this is over, a new mode is set.
2.3.5. Record Control Circuit Refer to Fig. 2.3.8 circuit diagram. RECORD mode is set by pressing Record Button, then Play Button together. By pressing Record Button, the Krec. signal becomes L, Q419 is turned ON, Q421 is turn ed ON, and the record lamp is illuminating. Then, by pres sing Play Button further, the Kplay signal becomes L,Q418 is turned ON, the PLAY signal becomes H (+24 VS), and Q420 is turned ON.
2.3.7. Control Motor Drive Circuit Refer to Fig. 2.3.10 circuit diagram and Fig. 2.3.11 timing chart. The control motor is turned by varying amounts, according to which control button is set. This motor is connected to the mechanism control cam, and the mechanism is set to the mode indicated by this cam. The motor is driven by the differential amplifier IC402 (1/2) and drivers Q405 and Q406. In the control motor stop condition, both voltages at pins No.5 (non-inverting input) and No.
2.3.8. Reel Motor Governor Refer to Fig. 2.3.12 circuit diagram. One end of the reel motor is connected with +12 V and the other end is a terminal for controlling. During FF mode, Q413 is turned ON and the reel motor is grounded. Accordingly, the reel motor turns in the direction of fast-forwarding. On the other hand, during REW mode, +24 V (REW H) is applied to the reel motor and the reel motor turns in the direction of rewinding.
3. REMOVAL PROCEDURES 3.1. Cassette Case Cover Ass’y Refer to Fig. 3.1. (1) Press the Eject Button to open the Cassette Case Ass’y. (‘2) Pull out F01 (Cassette Case Cover Ass’y) upwardly. 3.2. Top Cover Ass’y Refer to Fig. 3.1. Remove F02 and F03, then disassemble F04 (Top Cover Ass’y). 3.3. Bottom Cover Ass’y Refer to Fig. 3.1. Remove F05, then disassemble F06 (Bottom Cover Ass’y). 3.4. Front Panel Ass’y Refer to Fig. 3.2. (1) Refer to Fig. 3.1.
3.9. Main P.C.B. Ass’y Refer to Fig. 3.3. (1) Refer to Fig. 3.2. Remove Front Panel Ass’y referring to item 3.4. (2) Remove 5 connectors and the wires connected by wrapping from the F05 (Main P.C.B. Ass’y). (3) Remove F01, F02, F03, F04 and the Record Switch Linkage from the Wire Holder assembled with Record Switch, then disassemble F05 (Main P.C.B. Ass’y). 3.10. Control Switch Holder Ass’y Refer to Fig. 3.3. (1) Refer to Fig. 3.2. Remove Meter Ass’y referring to item 3.7.
3.14. Cassette Case Ass’y and Cover Plate Ass’y Refer to Fig. 3.5. (1) Refer to Fig. 3.2. Remove Mechanism Ass’y referring to item 3.6. (2) Press the Eject Button to open the Cassette Case Ass’y. (3) Remove F01, then disassemble the piston of the Pneumatic Damper Ass’y. (4) Remove F02 and F03 (Cassette Case Holder L Ass’y), then disassemble F04 (Cassette Case Ass’y). (5) Remove F05, then disassemble F06 (Cover Plate Ass’y). 3.15. Tape Counter Ass’y Refer to Fig. 3.5. (1) Refer to Fig. 3.2.
3.16. Capstan Motor Ass’y and Flywheel Ass’y Refer to Fig. 3.6. (1) Refer to Fig. 3.2. Remove Mechanism Ass’y referring to item 3.6. (2) Remove F01 and F02, then disassemble F03 (Fly wheel Holder Ass’y) and F08 (Capstan Belt). (3) Remove F04, then disassemble F05 (Capstan Motor Ass’y). (4) Remove F06, then disassemble F07 (Control P.C.B. Ass’y). (5) Remove F09 (Supply Flywheel Ass’y), then disassemble F10 (Take-up Flywheel Ass’y).
3.21. Cam Drive Gear and Control Cam Refer to Fig. 3.7. (1) Remove Sub Mechanism Chassis Ass’y referring to item 3.17. (2) Remove F20, then disassemble F21 (Cam Drive Gear). (3) Remove F22, then disassemble F23 (Counter-Load Arm Ass’y). (4) Remove F24, then disassemble F25 (Control Cam). 3.23. Pressure Roller Ass’y and Erase Head Refer to Fig. 3.8. (1) Remove Head Mount Base Ass’y referring to item 3.22. (2) Remove F03 and a washer, then disassemble F04 (Supply Pressure Roller Ass’y).
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5. MECHANICAL ADJUSTMENTS 5.1. Mechanism Control Cam Adjustment Before Adjustment, disassemble the Front Panel Ass’y then remove the Cover Plate Ass’y, referring to items 3.4 and 3.14. (1) Offset Adjustment of Control Motor Driver (a) Refer to Figs. 5.1 and 5.2. Adjust VR602 and VR603 on the Control P.C.B. to locate approximately at the middle of the variable range. Then turn ON the Power Switch.
2) 3) 4) 5) ference voltage in Fast (FF or REW) mode is changed. Therefore, re-check of the reference voltage in Fast (FF or REW) mode is required. If the reference voltage is out of the range, re adjustment of R414 according to next step 2) is necessary. Set the N-481 in FF mode, then adjust the value of R414 so that the voltage of VR601 will become lower by 1.5 V (±0.25 V) than in stop mode. Press the Pause Switch to set the N-481 in pause mode. Adjust the value of R454 to obtain 10 V (+0.4, -0.
5.3. Record Head and Playback Head Tilt Adjustment Note: On items 5.3 — 5.8, please refer to Fig. 5.4 flow chart. Refer to Figs. 5.5 and 5.6. (1) Load a Tilt Check Gauge M-9039 (DA09039A) in the N-481. (2) Clip the grounding terminal of the Tilt Check Gauge with one end of the cord with clip, and the other end to the chassis of the N-481. (3) Remove both of the Height Gears. (4) Set the N-481 in play mode.
5.5. Tape Guides Adjustment and Erase Head Stroke Adjustment Remove Head Mount Base Ass’y. Refer to Figs. 5.8 and 59. (1) Supply Tape Guide Height Adjustment (a) Load an EH Stroke Check Gauge M-9042/M-9051 in the N-481. (b) Set the N-481 in play mode. (c) Slide the Supply Tape Guide Check Bar down against the supply tape guide, thus check can be made on supply tape guide height. (d) If the supply tape guide is misaligned, the Supply Tape Guide Check Bar will not come into the supply tape guide.
5.6. Erase Head Height and Tilt Adjustment Refer to Figs. 5.10 and 5.11. (1) Remove Head Mount Base Ass’y referring to item 3.22. (2) Load an EH Tilt Check Gauge M-9040 (DA09040A) in the N481. (3) Set the N-481 in stop mode. (4) Check to insure whether one of the 3 Beacons is illuminating.
5.7. Playback Head and Record Head Height Adjustment and Azimuth Alignment Refer to Fig. 5.12. (1) Playback Head Height Adjustment and Azimuth Alignment (a) Connect a VTVM to the Output Jacks. (b) Load a 1 kHz Track Alignment Tape (DA09007A), then set the N-481 in play mode. (c) Turn the PH Height Gear until the output of both channels becomes minimum. (d) Load a 15 kHz Azimuth Tape (DA09004A), then set the N-481 in play mode.
5.8. Record Head Stroke Adjustment Refer to Figs 5.14 and 5.15. Note: This adjustment will be required only to insure freedom from misalignment of the record head stroke in the record head stroke check mode. (1) Check the accuracy of the record head stroke. (2) Remove Head Mount Base Ass’y referring to item 3.22. (3) Remove the record head assembly. (4) Adjustment of Record Head Mounting Gauge M-9048 (DA09048A) (a) Mount the Block B onto the Mounting Gauge Plate. (b) Loosen the 2 screws fixing the Block A.
5.9. Tape Travelling Adjustment The adjustment shall be made with a modified version of the current type EXII C-90 as shown in Fig. 5.16 (error will be made if a current type Tape Travelling Cassette (DAO9011A) should be used for this purpose). While modifying an EXII C-90, the tape guides in the cassette housing shall be kept protected to avoid tilt. Check shall be made in the following procedures: (1) An EXll C-90 Tape thus modified shall be loaded onto the N-481.
5.11. Flywheel Holder Adjustment (1) Refer to Fig. 5.18. Tighten the Thrust Screws until the gap between the Flywheel Assemblies and Thrust Screws becomes minimized when both of the Capstan Shafts are moved backwardly and forwardly (the Thrust Springs between the Capstan Flanges and Flywheel Thrust Caps are in a flat state). Excessive tightening of the Thrust Screws however will give damages on the Flywheel Assemblies, to which careful attention is invited. (2) Return the Thrust Screws by 1/2 turn.
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